In view of the environmental problems on the earth, fats and oils derived from animals and plants have been reviewed and the biofuels have been researched because they are considered to make carbon neutral and therefore lower the burden on the environments. The hydrocarbon obtainable from a green alga, Botryococcus braunii, which belongs to the microalgae is regarded as promising substitute for oil because pure hydrocarbons can be obtained by mass production (JP 2010-252700 A).
As another measure for the environmental problems, weight reduction of automobiles has been advancing in order to lower the greenhouse gas. In line with the weight reduction of automobiles, clutch or torque limiter mechanism is adopted in more parts and operated more frequently than conventional. Therefore, the clutch or torque limiter mechanism generally employs grease compositions where a silicone oil with excellent torque transmission performance, a traction oil such as synthetic naphthene oil or the like is used as the base oil (JP 3223210 and JP (Hei) 03-23593 B). However, the silicone oil-based grease has the problem of susceptibility to wearing, and on the other hand, the traction oil such as synthetic naphthene oil or the like has the problem of poor heat resistance. As the measures against wearing and low heat-resistance, use of squalene extracted from shark livers and squalane has been discussed (JP 2007-321042 A). Unfavorably, however, the traction coefficient of squalene or squalane is lower than that of the silicone oil or the traction oils such as synthetic naphthene oil or the like.
The automobiles are required to save energy, for example, to show good fuel efficiency. The lubricant is thus required to show low torque performance, and the base oil with low viscosity has been employed for the lubricant. However, the oil film obtainable from the low-viscosity oil becomes thin, which will impair the lubricating properties and reduce the life (flaking life). Then, the oil is required to contribute to the formation of a thick oil film even though the viscosity is low. Namely, the oil with a high viscosity-pressure coefficient (a) is needed. The recent research has demonstrated that base oils having high viscosity-pressure coefficient (a) are effective for preventing the bearings from electrical pitting (Proceedings of JAST Conference (Tokyo, 2011-5) of Japanese Society of Tribologists, p 239-240).